Electro discharge machining for one-way wire winding is an accurate mechanical machining method quickly developed in recent years. Electro machining was initially invented in 1943 by Mr. and Mrs. Lazarenko, scholars of the former Soviet Union, and later quickly developed along with improvement of the pulse power supply and control systems. Electro discharge machining is a special machining method, using electric corrosion that is generated when two electrodes immersed in the working solution performs pulse discharge there-between to corrode and remove conductive materials, so this technology is also called electric discharge machining.
In accordance with the shapes of the tool electrodes and the features of the relative movement between the tool electrodes and workpieces, electro discharge machining can be classified into five types: electro discharge cutting; electro discharge forming; electro discharge grinding; electro discharge conjugate revolution machining; hole machining, stamp marking, surface alloying, surface strengthening, etc. According to different wire winding speed, electro discharge cutting can be classified into quick electro discharge machining, intermediate electro discharge machining and one-way electro discharge machining. The present invention mainly describes the last electro discharge machining.
The development of the slow-wire-winding electric discharge machining (also called one-way-wire-winding electro discharge machining at home) is inseparable from the synchronous development of the cutting wire technology. Popular one-way wire winding lathes at present are designed according to the working features of the cutting line, and the breakthrough of the cutting line technology usually leads to innovation of the design of the line cutting machines. From the original oxygen-free copper wire cutting to the present cutting-line cutting, one-way wire-winding cutting experienced a very long time from low quality, low-efficiency production to high-efficiency, high-quality, automatic and specialized production. The line cutting technology in our country is developed on the basis of gradually importing overseas advanced technologies, from the earliest quick-wire-winding, intermediate-wire-winding to the present popular one-way-wire-winding electro discharge machining, experiencing a low-to-high development process. As mentioned above, the development of the cutting line technology determines the development direction of the cutting technology. To solve the task of how to research and develop the cutting line, the principle of electro discharge machining shall be understood first. During electro discharge machining, one electrode of the pulse power supply is connected with a tool electrode, and the other electrode is connected with a workpiece electrode. Both electrodes are immersed in a liquid medium with certain insulation (usually kerosene, mineral oil or deionized water; for the one-way-wire-winding cutting, deionized water is preferred). The tool electrode is controlled by an automatic feeding regulator to ensure that the tool and the workpiece maintain a very small discharge spacing (0.01˜0.05 mm) during normal machining. When a pulse voltage is applied between the two electrodes, the liquid medium at the nearest point between the two points is broken down in the current conditions, forming a discharge channel. Due to very small cross section of the channel and very short discharge time, the energy is highly concentrated (10˜107 W/mm), and the instant high temperature generated in the discharge area can melt and even evaporate the material to form electrically corroded pits. At end of the first pulse discharge, the second pulse breaks down and discharges at the nearest point at another electrode in a very short time period. Such cycle proceeds at a very high frequency. The tool electrode is continuously fed to the workpiece, and its moving shape is finally copied on the workpiece to form the required machining shape. At the same time, a small part of the total energy is released to the tool electrode, causing tool loss. The lost tool electrode is discharged continuously, while the new, intact tool electrode is fed without stopping, so the shape of the cutting tool electrode is kept at a dynamic balance, thus ensuring the dimensional accuracy and surface smoothness of the workpiece.
As the material machining technology and the mechanical machining technology are continuously improved, the cutting line experiences conversion from a common brass cutting line to clad cutting line, and even a multi-layer composite cutting line under research. The research of the clad cutting line all depends on the principle of the discharge machining. Coatings and coating structures of different compositions are applicable to the cutting of different types of materials.
For mechanical machining, the pursuit of accuracy is a main task at present. Production management personnel consider how to improve efficiency. For one-way-wire-winding discharge machining, the machining accuracy may be reduced while the speed is enhanced, and when the processing accuracy is improved, the processing efficiency is inevitably reduced. Therefore, the cutting line in the present invention is applicable to the cutting of irregularly shaped materials and those hollowed in the middle without affecting the processing accuracy, and the cut materials have high surface smoothness, with dimensional accuracy and form and location tolerance not lower than other types of one-way-wire-winding cutting line and with cutting speed improved.
The specific technologies of the cutting lines used at home and abroad are described below.
I. Common brass cutting line: Such cutting line is made of copper-zinc alloy. Limited by the zinc content in the brass, its cutting speed is restrained. As the zinc content in the brass increases, the cutting is enhanced a little, but the enhancement is limited because the higher the zinc content is, the bigger the processing difficulty is. Such a cutting line is usually employed by common users at home. If such a cutting line is used to cut irregularly shaped materials or those hollowed in the middle, the processing accuracy and surface quality will be restrained, and the cutting line is frequently broken, causing difficulty to the operations of the workers.II. Galvanized cutting line: Such cutting line uses common brass as the core and has a layer of zinc on the outside. Zinc performs gasification during cutting, so the discharge of such cutting line is relatively stable, and the cut surface is smoother than that of the common brass wire. Mature manufactures are mainly located in the EU. Some manufacturers in our country can produce such cutting line. However, such cutting line has a problem with dusting. Manufacturers at home and abroad all face such problem. Because of dusting, the auxiliary procedure time during cutting is prolonged, reducing the processing efficiency. When such electrode wire cuts irregularly shaped materials or those hollowed in the middle, zinc dusting is more serious.III. Speed type clad cutting wire: Such cutting line employs common brass as the core and copper-zinc alloy as the clad layer, which is a little bigger than that of the common galvanized cutting line. The speed of such clad cutting wire is higher than the cutting speed of the common galvanized cutting wire. Such cutting wire is applicable to high-efficiency machining. The core material of such cutting wire is common brass with relatively low tensile strength, so it is difficult to ensure the form and location tolerance during cutting.IV. β Cutting wire: Through research, it is found that cutting lines with uniform pits (cracks) can improve the discharge effect. To meet this need, such cutting with porous structure on the surface is generated. The core material of the diffusion annealing type cutting is oxygen-free copper or brass copper alloy and is covered with a layer of copper-zinc alloy on the outside through diffusion annealing, wherein the ratio of the copper and zinc is 1:1; the core material is oxygen-free copper or brass copper alloy, with the porous surface formed by diffusion annealing. The tissue of the surface material of the cutting line is β phase, therefore the cutting line is usually called β type cutting line. As everyone knows, the zinc content of the β phase is less than 50% at room temperature. The metal surface of the cutting line is β phase tissue. The β phase is brittle phase, so the roughness of the cutting line is poor, and such cutting line usually does not work or breaks when cutting irregularly shaped materials or those hollowed in the middle.. γ type cutting line: According to the research, the surface tissue is γ phase cutting line with high surface cutting accuracy, therefore the zinc content of the γ phase is about 60%. Such cutting line is called a γ type cutting line. The cutting line of such structure has a high zinc content and the electro discharge interval is small, so on the micro-level, the electro corroded pits are relatively small, and reflected on the macro-level, the cutting smoothness of this line is relatively high. On the other side, the γ phase has high zinc content, but the electric corroding speed of the zinc is relatively high, and zinc is quickly consumed in the cutting process. Likewise, the cutting line usually does not work or break when cutting the irregularly shaped materials or those hollowed in the middle.VI. Composite phase type cutting line: Such cutting line has β and γ phases on the surface and therefore is also called composite type cutting line. Such cutting line combines the advantages of the β and γ type cutting lines, and has cutting speed and cutting accuracy improved at the same time. Only a few industrially advanced countries in the world can produce such cutting line. The mixture of β and γ phases is required, so the manufacturing cost is relatively high. Because of the use cost, such cutting line is hardly used in the world.